Air pollution from automobile exhaust has grown progressively more serious with the increasing number of automobiles in use. Perhaps the major contributor is unburned hydrocarbons which are emitted during all engine operation, but are particularly heavy during idle, acceleration and deceleration operating regimes. Other air pollution products which are known to emanate from combustion engines are carbon monoxide and nitrous oxides (commonly designated as NO.sub.2 and collectively as NOX). One of the techniques which has been used to effect a reduction in emissions is to build engine mufflers including catalytic reactors, the catalyst used being typically a screen or exposed surface of a catalytic metal or compound such as vanadium or platinum or their oxides which aid in the combustion of the hydrocarbons. These devices have generally not been fully satisfactory, since the catalytic elements have tended to become poisoned by the pollutants or by the substances in the fuel, such as lead compounds, reducing their effectiveness in the cumulative process. Recent efforts to reduce or minimize lead in gasoline have been directed toward meeting this problem, but life of such catalytic elements is still definitely limited and periodic replacement is certainly an undesirable expense.
Another device which has been used to oxidize unburned carbon monoxide and hydrocarbons in exhaust devices is the afterburner. Afterburners, as they have been used in the prior art, are somewhat effective in reducing emissions, but, depending upon their particular configuration, suffer from a number of shortcomings and thus have never really proved sufficiently successful to become marketable. Control of temperatures has been a problem, and excessive temperatures have tended to cause unacceptably short life. While provisions have been made for providing air for combustion, this has usually not been controlled adequately. Frequently the resulting devices have been too heavy and bulky for reasonable installations and acceptable costs, especially where adequate means are included to insure acceptable exhaust temperatures.
More recent attempts to deal with engine emissions have led to different approaches, one being to resort to very careful tuning of the engine toward lean mixtures and the modification of valve and ignition timing. Such procedures reduce emissions significantly, but cause substantial losses in drivability and power output and require more frequent, exacting and expensive engine maintenance. Fuel economy usually also suffers. Another technique is to provide an engine-driven pump to inject air into exhaust passages to enable the unburned fuel to be burned in the exhaust manifold. This latter system is also effective to reduce emissions, but generally results in an increase in the emission of nitrogen oxides (NOX).
From the foregoing it is apparent that there is need for an exhaust gas processing system which is far simpler and more straightforward structurally than those presently in use and which is capable of reducing the emission of air polutants to acceptable levels. It is certainly preferable that such a system accomplish this objective without imposing penalties in operation of the associated engine, such as reduced power output, rough operation, higher heating loads, higher fuel consumption and lowered reliability.
An exhaust gas processing system which does much toward alleviating some of th aformentioned disadvantages is described in U.S. Pat. No. 3,577,728, issued May 4, 1971. In this patent a number of modifications are described, but the basic arrangement consists of an exhaust pipe from an engine which directs exhaust gas flow tangentially into a cylindrical reactor chamber such that the flow is directed in a vortical pattern. A low pressure area is created along the axis of the reactor chamber, and an inlet air port is located at the upstream end through which air is caused to enter the reactor because of the lowered pressure along its axis. Despite the inclusion of ignition devices such as glow plugs and/ or spark plugs, maintaining of flame propagation through all regimes of operation proves to be a problem with devices of this nature. It is pointed out in U.S. Pat. No. 3,577,728 that in dealing with unburned carbon monoxide and hydrocarbons, whether it be through the use of a catalytic muffler arrangement, pumps for supplying outside air into the exhaust manifold, or afterburners, it is necessary to complete the combustion of the unburned carbon monoxide and hydrocarbons, and this requires all of the following:
1. Sufficient time to permit the combustion to be completed. PA1 2. The maintenance of sufficiently high temperatures that combustion may be mantained over a long enough period to complete the combustion. PA1 3. Sufficient oxygen to support the combustion. PA1 4. Adequate means for mixing the added oxygen with the unburned hydrocarbons. PA1 5. Sufficient absolute pressure to support the combustion.
If any of the foregoing five requirements are not present to a sufficient extent, there will be a reduction in the effectiveness of the hydrocarbon combustion reaction. It is also true that the presence of one or more of these factors in a wrong proportion to the others can result in increasing the requirement for others. For instance, the presence of adequate oxygen but insufficient mixing means can substantially increase the amount of time required for satisfactory combustion. Similarly, the introduction of an excess amount of oxygen at low temperatures can lower the temperature in the combustion area sufficiently either to stop the combustion altogther or to inhibit it substantially such that much extra time is required.